The understanding of synaptic transmission and its modulation lies at the very center of our present understanding of brain function. The mechanisms of neurotransmission in synapses have been the subject of many classical studies in physiology. In recent years, several presynaptic proteins have been cloned and characterized by neurobiology research groups. One of the most pressing challenges in the field of synaptic transmission is to establish solid correlations between the roles of known presynaptic proteins and the physiological properties of depolarization-evoked secretion of transmitter. The proposed research aims at developing a model to study transmitter secretion in Xenopus oocytes. For this purpose, I will (1) expand pioneering work on the reconstitution of transmitter secretion in Xenopus oocytes, (2) use of a highly sensitive signal detection protocol consisting of detached, voltage-clamped myocytes and finally, (3) in the context of the reconstitution assay and physiological analysis, to dissect functional roles for cloned presynaptic proteins Synapsin, Synaptophysin, Synaptobrevin and Synaptoporin. The successful reconstitution of secretion mechanisms in oocytes will allow correlation of electrophysiological data with molecular manipulations that can be done in oocytes, not yet possible in other systems.